A hydroformylation reaction wherein linear (normal) and branched (iso) aldehydes in which the number of carbon atoms is increased by one are prepared by reacting various olefins with carbon monoxide (CO) and hydrogen (H2), commonly called synthetic gases, in the presence of a homogeneous organometallic catalyst and a ligand was firstly found by Otto Roelen in 1938 in Germany.
Generally, the hydroformylation reaction known as an oxo reaction is an industrially considerably important reaction in the homogeneous catalyst reaction, various aldehydes including about 8.40 million tons of alcohol derivatives are produced and used through an oxo process (SRI report, November 2002, 682. 7000A) in 2001.
Various aldehydes synthesized through the oxo reaction are converted into acid and alcohol as aldehyde derivatives through an oxidation or hydrogenation process. In addition, after condensation reaction of aldol or the like, aldehydes may be oxidized or hydrogenated and then converted into various acids and alcohols containing a long alkyl group. The alcohol hydrogenated from aldehyde, obtained by this oxo reaction, is referred to as an oxo alcohol. The oxo alcohol is industrially widely used for materials for solvents, additives, various plasticizers and synthetic lubricants.
A metal-carbonyl compound catalyst is known to be active as a catalyst of hydroformylation and the industrially used catalyst is generally based on cobalt (Co) and rhodium (Rh). N/I selectivity (ratio of normal to iso aldehyde) of produced aldehyde depends on the kind of catalyst and ligand, and operation conditions.
At present, 70% or more of oxo process throughout the world uses a low pressure oxo process in which an excess phosphine ligand is applied to a rhodium-based catalyst due to high catalyst activity, high N/I selectivity and relatively easy reaction conditions in spite of problems such as high catalyst cost and deterioration in catalyst activity caused by poisoning.
As a central metal of a catalyst for oxo reaction, a transition metal such as cobalt (Co) and rhodium (Rh) as well as iridium (Ir), ruthenium (Ru), osmium (Os), platinum (Pt), palladium (Pd), iron (Fe), and nickel (Ni) may be used. The respective metals exhibit catalyst activity in the order of Rh>>Co>Ir, Ru>Os>Pt>Pd>Fe>Ni.
Co, Rh, Pt and Ru are Group VIII transition metals, which exhibit superior catalystic activity during an oxo reaction. Pt and Ru are applied to only research application and most of oxo processes for commercial application are based on rhodium and cobalt, and representative examples thereof include HCo(CO)4, HCo(CO)3PBu3 and HRh(CO)(PR3)3.
Ligands used for oxo processes include phosphine (PR3, in which R represents C6H5 or n-C4H9), phosphine oxide and phosphite. Other ligands containing nitrogen include amines, amides, isonitrile and the like.
However, these ligands have considerably lower catalyst activity than that of ligands containing phosphine due to strong coordination of these ligands to metals thereof. In particular, when rhodium is used as a central metal, almost no ligands superior to triphenylphosphine (TPP) in terms of catalyst activity and stability are known.
Eastman Kodak and Union Carbide (incorporated into Dow Chemical) developed bidentate phosphine ligands that exhibit superior catalyst activity and high N/I selectivity (U.S. Pat. Nos. 4,694,109, 4,668,651), and Dow Chemical is known to apply bisphosphite ligands to some oxo processes.
Meanwhile, U.S. Pat. No. 4,668,651 discloses poly phosphite ligands represented by ligands B described in Examples 6 to 9, but these ligands exhibit considerably low N/I selectivity in spite of considerably superior catalyst activity.
An oxo reaction using phosphite as a ligand is disadvantageous in that the phosphite ligand is decomposed into alkyl phosphite, known as a catalyst poison, during the reaction, deteriorating reaction yield and increasing decomposition of ligand and catalyst.
Korean Patent No. 0198688 discloses a method for converting alkyl phosphite, which is produced as a catalyst poison from a phosphite ligand during a reaction, into a relatively inactive adduct by incorporating a weak acid compound, added water or an epoxide compound, or a method for reducing decomposition of the phosphite ligand. This method cannot satisfactorily improve catalyst yield and stability.